Complex One-to-many relation & Discriminator on many fie

BizuR · **Joined:** Tue May 16, 2006 3:41 am **Posts:** 5

Hibernate version: 3.1

Name and version of the database you are using: Oracle

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Hi everybody,

I'm actually working on an O/R mapping between an existing application and an existing database. And I meet some problems to map it correctly :

1/ I've got a first class called Risque, abstract, extended by two classes "RisqueA" and "RisqueB" and my inheritance strategy is "one table per concrete class" (so 2 tables here). the problem is those tables contains a same field which is a foreign key pointing on a table called Assurance (and which maps the class Assurance). My question is, How can I map the object Assurance which has an attribute with type "Risque" ?

2/ This time, I'm on a "one table per hierarchy"-strategy. I have to use a discriminator to identify which object has to be instanciated. However, one of my conditions has to refer to 3 differents fields on the datatable. Default discriminators allow to use only one field. But i read in the Hibernate documentation that we can use an attribute of discriminator called "formula"...
So, My questions are :
Can this attribute solve my problem ?
Or :
How do we use it ? And when ?
Do we use it in addition of the discriminator column ?
Or can we use it to replace the column"s attribute ?

Thanks in advance for all those who could help me solving those problem.

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

1) The association from Assurance to Risque should refer to Risque, not the subclasses. Hibernate will sort out the rest. There is nothing special that you have to to, it's just like having an association to a class with no subclasses.

2) Yes, it looks like formula is what you need. Put your SQL (not HQL) code in the formula. Subqueries are allowed. Case is more usual, though:

Code:

<discriminator type="int">
  <formula>
    case when (col1 > (col4 * 7) and col2 = 'test')) then 1
         when (col2 <> 'test') then 2
    else (select t.disc from table t where t.id = tableid)
    end
  </formula>
</discriminator>

Columns without prefixes used in the formula (tableid, in the example above) are from the main table: if you have a <join> you cannot use columns from it, and you also can't use columns from joined-subclass tables.

BizuR · **Joined:** Tue May 16, 2006 3:41 am **Posts:** 5

Thanks for your answer and sorry to do not have answered before... but i was working on another project... I gonna tried it this week but it seems the second problem is going to be solved :)

For the first one, I'm going to try it too :)

Thanks another time for your answer :)

BizuR · **Joined:** Tue May 16, 2006 3:41 am **Posts:** 5

Hi,
Thanks for your help, my inheritance is ok... excuse me for the time you wait before receiving your credit ;)